Time switch for photographic apparatus



Jan. 19, 1965 R. WICK ETAL 3,166,674

TIME SWITCH FOR PHOTOGRAPHIC APPARATUS Filed Oct. 26. 1961 IN V EN TOR.

BY RICHARD WICK OTHMAR SCHNEIDER United States Patent 15 Claims. 61. 25o217 The present invention concerns an electric time switch arrangementfor controlling the duration of exposures of photo-sensitive material toradiating energy. Arrangements of this type are most convenientlyapplied to apparatus for making photoprints in black and white or incolors, but it may as well be applied to apparatus for making X-raypictures.

Apparatus of the type to which the present invention is applicablecontain control means for limiting the exposure time in accordance with.the amount of radiating energy impinging during an exposure on thephoto-sensitive material. However, it is known that the expo-sure oflight sensitive material should additionally be controlled according tothe equation lt =constant, in which I indicates the intensity of theradiating energy or light impinging upon the light sensitivematerial, tis the time of exposure and p is the blackening exponent characteristicof the light sensitive material. This exponent p is well known in theart and may be equal to 1, larger than 1 or smaller than 1, dependingupon the particular material.

There are known arrangements of the type set forth which comprisedevices for taking the blackening exponent into account by correspondingadjustment or certain components of the arrangement.

However, it has been found that known arrangements of this type arecomparatively very involved in structure and require a great number ofindividual and delicate devices.

It is therefore a main object of the present invention to provide for anelectric time switch arrangement of the general type set forth whichprovides similar and more eflicient means for modifying the ordinaryexposure time control depending upon the characteristic blackeningexponent of the photo-sensitive material being used.

Other objects and characteristics of the invention will become apparentfrom the following description.

With above objects in view the invention provides in an electric timeswitch arrangement for controlling the duration of exposures ofphoto-sensitive material to radiating energy, in combination.

(a) Control means for limiting the exposure time in accordance with theamount of radiating energy impinging during an exposure on saidphoto-sensitive material, said control means including an electron tubecontrolling, upon being rendered non-conductive, the start, and uponbeing returned to conductive condition, the end of the exposure, theconductive condition of said tube depending upon a predeterminedpotential relation between two electrodes of-said tube, andphoto-responsive means exposed to said radiating energy and furnishingto one of said electrodes a potential gradually varying depending uponsaid India"- ing energy impinging on said photo-responsive means andthereby changing the potential and said one of said electrodes; and

(b) correction means for modifying the time limiting action of saidcontrol means, said correction means includ ing means for applying afirst predetermined potential to the other one of said electrodes,chargeable RC-circuit means having a predetermined charging timeconstant and being connected in circuit with said other one electrodefor changing said first potential at said other electrode depending uponthe charge potential of said RC-circuit 3,166,674 Patented Jan. 19, 1965means, and adjustment means for varying said charge potential inaccordance with the blackening exponent of the photo-sensitive materialbeing used, the superposition of said charge potential on said firstpotential applied to said other electrode by said correction meansmodifying the time period required for establishing said predeterminedpotential relation between said two electrodes and thus determining theduration of said conductive condition of said electron tube and therebythe duration of the exposure.

In a preferred embodiment of the invention the RC- circuit meanscomprise at least two RC-circuits having time constants differing fromeach other, the capacitors of all of these RC-circuits being connectedin series.

It is particularly recommended to connect in a twocapacitor arrangementone of the capacitors with one electrode, preferably with the cathode,of an electron tube forming part of the ordinary time controlarrangement, and to connect the othercapacitor with the movable tap of apotentiometer. In this case the electron tube and a control relaycontrolled thereby may be arranged in a separate control circuit, whilethe above mentioned potentiometer forms part of the timing circuit ofthe time control arrangement, whereas the capacitors of the abovementioned RC-circuits are arranged in a separate adjustment circuit,each of these circuits having preferably separate power supply circuits.The potentiometer arranged in the timing circuit may be connected inparallel with a series combination comprising conventional photocell andtiming capacitor of the timing arrangement.

As a further advantageous characteristic of the invention the means forchanging the potential applied to one electrode of the electron tube areconnected with the respective power supply in such a manner that thepolarity of the potential derived from the adjustment means can bereversed. For this purpose a potentiometer is included in the chargingcircuit of each of the capacitors of the RC-circuits, each capacitorhaving one terminal connected with a fixed center tap of the respectivepotentiometer, while the other terminal of the capacitor is connectedwith the movable tap of that potentiometer. It is advisable to couplemechanically the movable taps of these potentiometers. It is furtherrecommended to arrange the justmentioned potentiometers so that they areconnected in parallel with each other and that their movable taps, whenmoved simultaneously, have an opposite effect on the respectivepotentiometers. In addition it is desirable to couple mechanically thetwo movable taps of the above mentioned potentiometers also with themovable tap of the previously mentioned potentiometer located in thetiming circuit. Finally, all these movable potentiometer taps mentionedabove may be controlled by one single control knob having an indexcooperating with a corresponding scale.

If the invention is applied to photographic printing apparatus used formaking color prints and therefore requiring a plurality of colorcomponent exposures, a corresponding plurality of arrangements accordingto the invention may be provided.

It is a remarkable advantage of the arrangement according to theinvention that the adjustment of the exposure time in view of theblackening constant of the material being used is carried outexclusively by a group of potentiometers cooperating with thecorresponding RC- circuits. It is further to be noted that thearrangement according to the invention requires very little electricalenergy while nevertheless offering a very great range of adjustment. Thevoltage characteristic of the adjustment means corresponds verysatisfactorily with the desired adjustment values within the abovementioned great range of adjustment.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing, inwhich an embodiment of the invention is illustrated in the form of aschematic circuit diagram.

It will be understood that the arrangement according to the invention asillustrated applies to a photographic printing apparatus, not shown,having a light source 1 connected by lines 2 and 3 with a general supply4, 5 of alternating current, controllable by a main switch 6. The mainpurpose of the arrangement described below is to control the duration ofan exposure of photo-sensitive material to the radiating energyfurnished by the light source 1. The arrangement according to theinvention as shown comprises three main circuits, namely a light controlcircuit 7, a time control circuit 8 and an adjustment circuit 9. Each ofthese circuits comprises a separate power supply circuit 10, 11, 12,respectively. These supply circuits 1'0, 11 and 12 obtain energy throughsecondary windings 13, 14 and 15, respectively, of a transformer 16having a primary 17 connected to the main power supply 4, 5. The powersupply circuit co. prises in conventional manner a four-way rectifier 18and a filter circuit composed of the capacitors 19 and 2t) and aresistor 21. The power supply circuits 11 and 12 are constructed in thesame manner.

The light control circuit 7 comprises in series arrangement a controltube 22, preferably a thyratron, a relay coil 23 operating, amongothers, a relay switch 23a in the connection 3 of the light source 1,and a starter switch 24 movable between two stationary contacts 25 and26 for the purpose of briefly interrupting the light control circuit 7when the switch 24 is moved from one of the contacts 25, 26 to theother. The time control circuit 8 comprises a conventional timingcapacitor 27 connected in series with a photocell 28 which is arrangedto be exposed to the radiating energy furnished by the light source 1and impinging on the photo-sensitive material. The junction point 29between the capacitor 27 and the photocell 28 is connected via line 30with the control grid 31 of the tube 22. A relay switch 23b operable bythe coil 23 is connected in parallel with the capacitor 27 so that thelatter is shunted when switch 23b is in closed position.

The photocell 28 may be an electron multiplier phototube. It operates inthe well known manner.

The adjustment circuit 9 comprises two RC-circuits 32, 33 and 34, 35.The capacitors 32 and 34 of these circuits are connected in series andthe pertaining adjustable resistors 33 and 35 are arranged, as shown, inseparate charging circuits for the respective capacitors 32 and 34. Thecapacitors 32 and 34 can be charged with potentials determined by thepotentiometers 36 and 37, respectively, which are connected in parallelbetween the supply lines 38 and 39 connected with the supply circuit 12and carrying direct current voltage. The junction point 40 between thecapacitors 32 and 34 is connected by a line 41 with both the fixedcenter taps 42 and 43 of the potentiometers 36 and 37, respectively. Theresistors 33 and 35, however, are connected via lines 44 and 45,respectively, with the movable potentiometer taps 46 and 47,respectively.

A relay switch 23c is connected in parallel with the capacitor 32, andsimilarly a relay switch 23d is connected in parallel with the capacitor34. Both these last mentioned relay switches are also operated by therelay coil 23.

The capacitor 32 is connected by the line 48 with the cathode 49 of thecontrol tube 22 of the light control circuit 7, while the capacitor 34is connected by line 50 with the movable tap 52 of the potentiometer 51of the time control circuit 8. The potentiometer 51 is connected acrossthe supply lines 53 and 54 of the power supply circuit 11 and at thesame time in parallel with the seriescombination consisting of thetiming capacitor 27 and the photocell 28. The movable tap 52 of thepotentiometer 51 is mechanically coupled with the movable taps 46 and 47of the potentiometers 36, 37 of the adjustment circuit 9, e.g. by meansof a common shaft 55 indicated only symbolically by dash-dotted lines inthe drawing and turnable by means of a control knob 56. This knob isequipped with an index or pointer 57 which cooperates with an adjustmentscale or graduation 58 that may be arranged on the outside wall of theprinting apparatus not shown in the drawing.

For describing the operation of this arrangement, it may be assumed thatthe printing apparatus is to be operated While the control knob 56 andaccordingly the potentiometer taps 46, 47 and 52 are in the positionshown in the drawing.

It is to be understood that, as long as the main switch 6 is in openposition, the relay switch 23a is in closed position, the relay switches23b, 23c and 23d are in open position, and no potential differenceexists between the grid 31 and the cathode 49 of the tube 22.

Consequently, upon closing the main switch 6 the tube 22 is immediatelyrendered conductive and causes energization of the relay coil 23 wherebythe relay switch 23a is moved to open position and the relay switches23b, 23c and 23d are moved to closed position. This means that theserelay switches are in the positions shown in the drawing as soon as thetime switch arrangement according to the invention is ready foroperation. Under these circumstances the cathode 49 of the tube 22 isprovided across the switches 23c and 23d of the shunted capacitors 32,34 with a potential available at the movable tap 52 of the potentiometer51, while the grid 31 remains on ground potential and has therefore anegative potential with respect to the cathode 49 following the changeof tube 22 to conductive condition. Nevertheless, in view of thewell-known characteristics of a thyratron the tube 22 remains inconductive condition so that also the relay coil 23 remains in energizedcondition.

If now an exposure of the photo-sensitive material is to be carried outthe starting switch 24 is moved from the position contacting the contact25 to its second position contacting the contact 26. The movement of theswitch 24 causes a transitory interruption of the circuit whereby thetube 22 is changed to non-conductive condition, the relay coil 23 isde-energized so that relay switch 23a moves to closed position while therelay switches 23b, 23c and 23d are moved to open position. By theclosing of relay switch 23a the source of light 1 is switched on and theexposure of the photo-sensitive material is started. At the same timecharging of the capacitors 32 and 34 is started and continues until thecapacitor 32 assumes the potential existing between the center tap 42and the movable tap 46 of the potentiometer 36, and until the capacitor34 assumes the potential existing between the center tap 43 and themovable tap 47 of the potentiometer 37. Since the capacitors 32 and 34are connected in series and since the positioning of the movable taps46, 47 of the potentiometers 36, 37, respectively, in relation to theircenter taps 42, 43, respectively, occurs in mutually oppositedirections, the charging potentials of the capacitors 32 and 34 aresuperimposed on each other and simultaneously added to the potentialtapped from the potentiometer 51, so that the potential at the cathode49 of the tube 22 is gradually increased in accordance with the chargingrate of the capacitors 32, 34, starting with the potential of themovable tap 52, from the start of the exposure on- Ward.

Independently, the timing capacitor 27 of the time control circuit 8 isalso charged by the photo-current of the photocell 28 illuminated by theradiating energy furnished by the source 1, the charge potential of thecapacitor 27 being applied to the grid 31 of the tube 22 via the line30. I

As soon as the potential of the grid 31 of the tube 22 reaches thecathode potential, the tube 22 is rendered conductivewhereby the relaycoil 23 is returned to energizedv condition and the relay switches 23a,23b, 23c and 23d are returned to the positions shown in the drawing.Hereby the source of light 1 is switched off and the exposure isterminated While the capacitors 27, 32 and 34 are shunted and thusdischarged. Consequently, the potential of the cathode 49 of the tube 22drops back to the potential of the movable tap 52 of the potentiometer51 while the grid 31 assumes again groundpotential. However, the tube 22remain in conductive condition and the relay coil 23 remains inenergized condition. In this manner the time switch arrangement is nowready for another cycle of operations, i.e. for another exposure.

The gradual raising of the cathode potential of the tube 22 inaccordance with the charging of the capacitors 32, 34 has the effectthat-relative to a medium exposure'time selected for the purpose ofcalibration exposure times of comparatively long duration can beextended still further and exposure times of comparatively shortduration can be shortened still further. The relation between theadjustable resistors 33 and 35 and the associated capacicumstances theRC-circuit with the shorter charging time causes a substantial increaseof the potential at the cathode 490i the tube 22 during the firstportion of an exposure, while the RC-circuit with the longer chargingtime causes the potential rise at the cathode 49 to continue for alonger period commencing with the start of the exposure. Neverthelessthe operating voltages involved remain comparatively low. The chargingtimes of the RC-circuits containing the capacitors 32, 34 can be variedby adjustment of the resistors 33, 35, respectively, and can be adjustedarbitrarily with respect to each other.

As a whole, the potential rise at the cathode 49 of the tube 22 duringan exposure can be varied by corresponding setting of the control knob56 and is increased by turning the knob 56 in counter-clockwisedirection. By turning the knob 56 and the shaft 55 increasing portionsof the upper half of the potentiometer 36 and of the lower half of thepotentiometer 37 are introduced into the charging circuits of thecapacitors 32 and 34, respectively, whereby the maximum chargepotentials of these capacitors are increased, while simultaneously thestarting potential of the cathode 49 is reduced due to the simultaneousturning of the movable tap 52 of the potentiometer 51.

However, if the control knob 56 is turned in opposite direction untilits index 57 registers with the center mark 59 of the graduation 58 thestarting potential of the cathode 49 is raised to a potentialcorresponding to the center point of the potentiometer 51 while themovable taps 46, 47 are positioned in register with the center taps 42,43, respectively, whereby the otentiometers 36, 37, respectively, arecompletely eliminated from the charging cir-v cuits of the. associatedcapacitors 32, 34, respectively. In this case the capacitors 32, 34 arenot charged at all at the beginning of, and during, an exposure so thatthe potential at the. cathode 49 of the tube 22 remains constantirrespective of the duration of an exposure. 8

If the control knob 56 is turned further in clockwise direction portionsof the lowerhalf of the potentiometer 36 and portions of the upper halfof the potentiometer 37 ode 49. Consequently, in this case the potentialof the.

cathode 49 of thetube 22 is decreased with increasing exposure time andthe starting potential of the cathode 49 and the degree of potentialdecrease are both increased,

with increasing turning of the control knob 56 in clockwise direction.

It can be seen therefore that the blackening exponent characteristic ofthe photo-sensitive material being used can be taken into account byusing the arrangement according to the invention. This applies both toblackening exponents smaller than 1 as well as to blackening exponentsequal to 1 or larger than 1. In using the arrangement described above itis advisable to take into account not only the blackening exponent ofthe photosensitive material being used but also a possibly existingmismatch between the photocell 28 and the photo-sensitive material. Sucha mismatch exists when the spectral sensitivity of the photocell 28 doesnot agree with the spectral sensitivity of the photo-sensitive ma erial.It occurs frequently that the sensitivity of the photocell extends overa wider spectral range than that of the, photo-sensitive materal whichcondition is called under-matching. The opposite condition is calledover-matching. The effect of a mismatch is similar to that defined bytheblackening exponent, namely in the case of under-matching long exposuretimes are too short andshortexposure times are too long, while theopposite is the effectof over-match ing. However, also these efiects canbe taken into account together with the blackening exponent bycorrespondingly setting the control knob for determining the desiredcorrection of the exposure time.

it is of particular importance to take into account the blackeningexponent and a mismatch between the lightsensitive member and thephoto-sensitive material in the case of making color prints. In thiscase it is possible that different blackening exponents apply 'to thedifferent layers or" the color print material sensitive to light ofdifferent basic colors. Also the character and degree of a mismatchbetween the light-sensitive member and the color print material maydiffer for different basic colors so that in the production of colorprints notonly wrong densities but also wrong colors may result if theblackening exponent and a mismatch are not taken into account.

Inorder to avoid such undesirable results it is adaccording to theinvention it is possible to take intoaccount the blackening exponent foreach differently color-sensitive layer of the color print materialand-to take into account the character and degree of a mismatch of thephotocell. with the color-sensitivity of each layer of the material.

The time switch arrangement according to the invention-can also beapplied advantageously to color printing apparatus in which, e.g. inaccordance with the French Patent 1,173,295, the individual componentcolor exposures are carriedout in sequence with the use of additivefilters and with a single exposure control device used repeatedly duringa complete color printing operation. In this case the arrangement asdescribed and illustrated may be modified in such a manner that thepotentiometer taps 46, 47, 52 are moved automatically into predeterminedpositions before the start of each indi vidual component exposure.

Of course, the arrangement as described and illustrated may be modifiedin various respects. For instance, the two RC-circuits 32, 33 and 34, 35in the adjustment i) circuit 9 may be supplemented by additionalRC-circuits having time constants diilering from the time constants ofthe other RC-circuits. In such case it is advisable to connect also thecapacitors of the additional RC-circuits in series with the capacitors32, 34.

Each of the potentiometers 36, 37 having fixed center taps 42, 43 andmovable taps 46, 47, respectively, is Well suited for reversing thepolarity of the means influencing the cathode potential of the tube 22also if only one capacitor is used instead of a plurality of capacitors32, 34, Generally it is advisable to use one single device forproducing, by polarity reversal, an increase as Well as a decrease ofthe potential of the cathode 49 of the tube 22.

The start and termination of an exposure may be effected, instead ofswitching on and off the light source 1, also in such a manner that thelight source 1 is left witched on continuously while a shutter arrangedacross the path of the radiating energy furnished by the source 1 isopened and closed by means of electromagnetic means controlled by therelay coil 23.

The capacitor 32 or" the adjustment circuit 9 may be connected, insteadof to the cathode 49 of tube 22, also to another electrode of the tube,e.g. to a screen grid not shown in the drawing but existing in aditierent type of'a control tube in which case of course a correspondingchange of poential at the capacitors 32, 34 is to be providcd.

Finally, it is to be borne in mind that the time switch arrangementaccording to the invention is applicable not only to photographicprinting apparatus but also to other devices, e.g., X-ray pictureapparatus.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofan electric time switch arrangement differing from the types describedabove.

While the invention has been illustrated and described as embodied in anelectric time switch arrangement for controlling the duration ofexposures of photo-senstitive material to radiating energy, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications Without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In an electric tirru'ng arrangement for controlling the duration ofexposures of photo-sensitive material to radiating energy, incombination, means for interrupting the exposure of said material tosaid radiating energy, an electron tube controlling said exposureinterrupting means in dependence of a conductive condition of said tubewhereby said conductive condition itself depends upon a predeterminedpotential. relation between two electrodes of said tube, a firstcondenser connected to one of said electrodes of said tube, means forvarying the electric charge of said first condenser during the exposure:of said material, means for applying a first predetermined potential tothe other one of said electrodes, and correction means for modifying thetime limiting action of said timing arrangement, said correction meansincluding at least two RC-circuit means including second capacitors,respectively, means which at the beginning of the exposure periodcommence the bringing about of the charging of each of said secondcapacitors to respective predetermined charge potential condition, andmeans for varying the electric charge of each of said second capacitorsduring the exposure of said material, each or" said RC-circuit meanshaving a predetermined charging time constant different from that of theother one and said second capacitors being connected in series with eachother and in circuit with said other one of said electrodes for changinsaid first potential applied to said other electrode in accordance withthe change of charge potentials of said second capacitors during theexposure of said material.

2. In an electric time switch arrangement for controlling the durationof exposures of photo-sensitive material to radiating energy furnishedby a source of such radiating energy, in combination, control means forlimiting the exposure time in accordance with the amount of radiatingenergy impinging during an exposure on said photosensitive material,said control means including an electron tube controlling, upon beingrendered non-conductive, the start, and upon being returned toconductive condition, the end of the exposure, the conductive conditionof said tube depending upon a predetermined potential relation betweentwo electrodes of said tube, and photoelectric means exposed to saidradiating energy and furnishing to one of said electrodes a potentialgradually varying depending upon said radiating energy impinging on saidphoto-electric means and thereby changing the potential at said one ofsaid electrodes; and correction means for modifying the time limitingaction of said control means, said correction means including means forapplying a first predetermined potential to the other one of saidelectrodes, at least two chargeable RC-circuit means includingcapacitors, respectively, connected in series with each other, each ofsaid RC-circuit means having a predetermined charging time constantdifferent from that of the other one and being connected in circuit withsaid other one electrode for changing said first potential at said otherelectrode depending upon the charge potentials of said RC-circuit means,means which at the beginning of the lighting period commence thebringing about of the charging of each of said capacitors to arespective predetermined charge potential condition, and adjustmentmeans for varying said charge potentials in accordance with theblackening exponent of the photosensitive material being used, thesuperposition of said charge potentials on said first potential appliedto said other electrode by said correction means modifying the timeperiod required for establishing said predetermined potential relationbetween said two electrodes and thus determining the duration of saidconductive condition of said electron tube and thereby the duration ofthe exposure.

3. In an electric time switch arrangement for controlling the durationof exposures of photosensitive material to radiating energy furnished bya source of such radiating energy, in combination, control means forlimiting the exposure time in accordance with the amount of radiatingenergy impinging during an exposure on said photo-sensitive material,said control means including an electron tube controlling, upon beingrendered non-conductive, the start and, upon being returned toconductive condition, the end of the exposure, the conductive conditionof said tube depending upon a predetermined potential relation betweenthe cathode and at least one of the electrodes of said tube, andphoto-electric means exposed to said radiating energy, and capacitormeans constituting .a series-combination with said photo-electric means,said series-combination furnishing to one of said electrodes a potentialgradually varying depending upon said radiating energy impinging on saidphotoelectric means and thereby changing the potential at said one ofsaid electrodes; and correction means for modifying the time limitingaction of said control means, said correction means includingpotentiometer means for applying a first predetermined. potential tosaid cathode, at least two chargeable RC-circuit means including secondcapacitor means, respectively, connected in series with each other, eachof said RC-circuit means having a predetermined charging time constantdifierent from that of the other one and one of said second capacitormeans being connected in circuit with said cathode, and the other one ofsaid second capacitor means being connected with the movable tap of saidpotentiometer means for changing said first potential at said cathodedepending upon the charge potentials-of said RC-circuit means, meanswhich at the beginning of the lighting period commence the bringingabout of the charging of each of said capacitors to a respectivepredetermined charge potential condition, and adjustment means forvarying said charge potentials in accordance with the blackeningexponent of the photosensitive material being used, the superposition ofsaid charge potentials on said firstpotential applied to said cathode bysaid correction means modifying the time period required forestablishing said predetermined potential relation between the cathodeand at least one of the electrodes and thus determining the duration ofsaid conductive condition of said electron tube and thereby the durationof the exposure.

4. An arrangement according to claim 3, comprising a control circuitincluding a first power supply unit, said electron tube and relay meanscontrolled by said electron tube and controlling the source of radiatingenergy, further comprising a time control circuit including a secondpower supply unit, said photo-electric means, said first capacitor meansand said potentiometer means, and further comprising an adjustmentcircuit including a third power supply unit and said RC-circuit means.

5. An arrangement according to claim 4, wherein said potentiometer meansare connected in parallel with said series-combination of photo-electricmeans and first capacitor means.

v 6. An arrangement according to claim 5, wherein said correction meansinclude means for reversing the polarity of said first predeterminedpotential with respect to an intermediate potential value. 7. Anarrangement according to claim 6, wherein said adjustment means includea first and a second control potentiometer connected in parallel witheach other and in circuit with said second power supply unit, one ofsaid RC-circuit means being connected between a fixed intermediatetapping point and the movable tap of said first control potentiometer,the other one of said RC-circuit means being connected between a fixedintermediate tapping point and the movable tap of said second controlpotentiometer.

8. An arrangement according to claim 7, wherein said movable taps ofsaid first and second control potentiometers are mechanically coupledwith each other and jointly controllable.

9. An arrangement according to claim 8, wherein said first and secondcontrol potentiometers and their respective movable taps are so arrangedthat joint movement of said movable taps has opposite adjustment effecton the respective control potentiometers.

10. An arrangement according to claim 8, wherein said movable taps ofsaid first and second control potentiometers and the movable tap of saidpotentiometer means controlling said photo-electric means are allmechanically coupled with one another and jointly controllable.

11. An arrangement according to claim 10, including control means forcontrolling all of said movable taps and including indexing means fordetermining the adjustment of said taps.

12. In an electric timing arrangement for controlling the duration ofexposures of photo-sensitive material to radiating energy, incombination, means for interrupting the exposure of said material tosaid radiating energy, an electron tube controlling said exposureinterrupting means in dependence of a conductive condition of said tubewhereby said conductive condition itself depends upon a predeterminedpotential relation between two electrodes of said tube, a firstcondenser connected to one of said electrodes of said tube, means forvarying the electric charge of said first condenser during the exposureof said material, potentiometer means for applying a first predeterminedpotential to the other one of said electrodes, said potentiometer meansincluding a resistance connected with a power supply circuit and a tapmovable along said resistance and connected with said other one of saidelectrodes, and correction means for modifying the time limiting actionof said timing arrangement, said correction means including at least twoRC- circuit means including second capacitors, respectively, means whichat the beginning of the exposure period commence the bringing about ofthe charging of each of said second capacitors to a respectivepredetermined charge potential condition, and means for varying theelectric charge of each or said second capacitors during the exposure ofsaid material, each of said RC-circuit means having a predeterminedcharging time constant different from that of the other one and saidsecond capacitors being connected in series with each other and incircuit between said movable tap of said potentiometer means and saidother one of said electrodes for changing said first potential appliedto said other electrode in accordance with the change of chargepotentials of said second capacitors during the exposure of saidmaterial.

13. An arrangement according to claim 12, comprising a relay arranged inthe circuit of said electron tube, and switches each of them shuntingone of said first and second condensers, respectively, said switches andsaid exposure interrupting means being controlled by said relay.

14. An arrangement according to claim 3, wherein said adjustment meansfor varying said charge potentials are constructed for simultaneouslychanging, when desired, also the polarity of said charge potentials.

15. An arrangement according to claim 7, wherein each of said first andsecond control potentiometers has two portions extending in oppositedirection from the respective fixed intermediate tapping point thereof,the outer ends of said first and second control otentiometers beingconnected with the terminals, respectively, of said third power supplyunit so that also the polarity of said variable charging potentials ofsaid RC-circuit means is changeable depending upon whether said movabletaps of said control potentiometers are moved from said intermediatetapping point in one or the other direction over said portions thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,078,677 4/37Long 250-217 X 2,472,815 6/49 Fleming 250-205 2,749,799 6/56 Strem250-217 2,885,563 5/59 Batina et a1 250-405 2,929,000 3/60 Arrison 2502,993,124 7/61 Graves et al. 25095 3,033,988 5/62 Edgerton 250205 IFOREIGN PATENTS 564,500 9/ 44 Great Britain. 7 06,671 3 54 GreatBritain.

RALPH G. NILSON, Primary Examiner.

1. IN AN ELECTRIC TIMING ARRANGEMENT FOR CONTROLLING THE DURATION OFEXPOSURES OF PHOTO-SENSITIVE MATERIAL TO RADIATING ENERGY, INCOMBINATION, MEANS FOR INTERRUPTING THE EXPOSURE OF SAID MATERIAL TOSAID RADIATING ENERGY, AN ELECTRON TUBE CONTROLLING SAID EXPOSUREINTERRUPTING MEANS INDEPENDENCE OF A CONDUCTIVE CONDITION OF SAID TUBEWHEREBY SAID CONDUCTIVE CONDITION ITSELF DEPENDS UPON A PREDETERMINEDPOTENTIAL RELATION BETWEEN TWO ELECTRODES OF SAID TUBE, A FIRSTCONDENSER CONNECTED TO ONE OF SAID ELECTRODES OF SAID TUBE, MEANS FORVARYING THE ELECTRIC CHARGE OF SAID FIRST CONDENSER DURING THE EXPOSUREOF SAID MATERIAL, MEANS FOR APPLYING A FIRST PREDETERMINED POTENTIAL TOTHE OTHER ONE OF SAID ELECTRODES, AND CORRECTION MEANS FOR MODIFYING THETIME LIMITING ACTION OF SAID TIMING ARRANGEMENT, SAID CORRECTION MEANSINCLUDING AT LEAST TWO RC-CIRCUIT MEANS INCLUDING SECOND CAPACITORS,RESPECTIVELY, MEANS WHICH AT THE BEGINNING OF THE EXPOSURE PERIODCOMMENCE THE BRINGING ABOUT OF THE CHARGING OF EACH OF SAID SECONDCAPACITORS TO A RESPECTIVE PREDETERMINED CHARGE POTENTIAL CONDITION, ANDMEANS FOR VARYING THE ELECTRIC CHARGE OF EACH OF SAID SECOND CAPACITORSDURING THE EXPOSURE OF SAID MATERIAL, EACH OF SAID RC-CIRCUIT MEANSHAVING A PREDETERMINED CHARGING TIME CONSTANT DIFFERENT FROM THAT OF THEOTHER ONE AND SAID SECOND CAPACITORS BEING CONNECTED IN SERIES WITH EACHOTHER AND IN CIRCUIT WITH SAID OTHER ONE OF SAID ELECTRODES FOR CHANGINGSAID FIRST POTENTIAL APPLIED TO SAID OTHER ELECTRODE IN ACCORDANCE WITHTHE CHANGE OF CHARGE POTENTIALS OF SAID SECOND CAPACITORS DURING THEEXPOSURE OF SAID MATERIAL.